The present invention is in the field of programmable logic controller (PLC) systems which control a wide variety of manufacturing processes. A typical configuration is shown in FIG. 1, and comprises a power supply 11 which supplies power to a processor 13 which is coupled to an address bus 20, a data bus 22 and control bus 24, each of which are coupled to individual controller slots 15. As shown in FIG. 1, a single processor or PLC typically accesses up to 16 controller cards coupled directly thereto through a backplane 31, each of which is plugged into one of the controller slots 15. The controller cards themselves interface, for example, external apparatus such as robots on an assembly line through input cards for receiving signals from the robots and output cards for generating signals which control the operation of the robots through a feedback control loop. Another type of external apparatus which may be controlled by a PLC is a resistance welding machine which is itself controlled by a controller such as that disclosed in U.S. Pat. No. 4,456,809. However, such weld controllers are typically stand alone units or if coupled to a PLC, then such coupling is through a set of cables which are then connected to an input card and an output card which are mounted in a slot.